Air-cooled coaxial line termination



April 1967 v H. E. STEVENS 3,312,926

AIR-COOLED COAX IAL LINE TERMINATION III INVENTOR. HAROLD E. STEVENS KITTOENEYS April 4, 1967 H. E. STEVENS I AIR-COOLED COAXIAL LINE TERMINATION 2 Sheets-$heet 2 Filed June 17, 1965 INVENTOR. HAROLD E. 5TEVEA/5 ATTOEA/fEYS.

United States Patent 3,312,926 AIR-COGLED COAXIAL LINE TERMINATION Harold E. Stevens, Lyndhurst, Ohio, assignor to Bird Electronics Corporation, Solo, ()hio, a corporation of Ohio Filed June 17, 1965, Ser. No. 464,621 11 Claims. (Cl. 338-216) This invention relates to a coaxial line termination, and more particularly, to an improved coaxial line electrical termination.

Among the principal objects of the invention are the provision of a coaxial line termination which is compact in construction employing relatively few parts and providing substantially refiectionless termination while converting relatively large amounts of electrical energy into heat.

These and other various other objects and features of the invention will be more clearly understood from a reading of the detailed description of the invention in conjunction with the drawing, in which:

FIG. 1 is a side elevational view of an end of a coaxial line and a termination according to one illustrative embodiment of this invention;

FIG. 2 is a plan view partly in section taken along the lines 22 of FIG. 1;

FIG. 3 is an end view of the line termination and coaxial connector of FIG. 1 with the coaxial line disco-nnected; and a FIG. 4 is an end view, to an enlarged scale, of the spring-conductor assembly, of FIG. 3, as viewed from the coaxial line connector.

Referring now to the drawing and particularly to FIGS. 1 and 2 thereof, a coaxial line termination in accordance with one illustrative embodiment of this invention, is connected to a coaxial line 12 by means of a coaxial connector 13. This connector may be of the type disclosed in Bird et al. Patent No. 2,966,645, issued Dec. 27, 1960. The coaxial connector 13 includes a threaded sleeve 14 and a base assembly including a cylindrical section 16 and an integral depending flange 17. The threaded sleeve 14 is rotatably mounted on a cylindrical section 16 by means of a flange, not shown, and connects with the outer coaxial conductor. Connector 13 is mounted on termination 10 by means of the depending substantially square flange 17 through which a plurality of screws 18 pass and threadably engage a mounting ring 20 forming an end portion of a load resistor housing 22. The mounting ring 20* is held in the load resistor housing 22 and is given an axial thrust by means of a beveled C-shaped retaining ring 23', shown in section in FIG. 2. The C-shaped retaining ring is radially inwardly stressed prior to insertion into an annular notch 24 in the load resistor housing 22. When the stress is released the beveled surface engages notch 24 and imparts an axial thrust forcing the mounting ring 20 in snug abutting relationship with a shoulder 25 of the load resistor housing 22. The mounting ring 20 is provided with an annular notch 26 which compressively receives an O-ring 27 between the mounting ring 20 and the load resistor housing 22 to provide a vapor seal.

Preferably, the housing 22 is generally cylindrical and is solid metal which constitutes a good heat conduction path to the radiators which will be subsequently described. The load resistor housing 22 is preferably formed of a material having a high thermal conductivity and in this particular instance, the resistor housing is formed of metal such as aluminum. A radiator assembly 30 is mounted on resistor housing 22 for radiating generated thermal energy to the ambient air.- Radiator assembly 30 includes a plurality of circular rings 32 which are forced onto and snugly engage the periphery of the load resistor housing 3,312,926 Patented Apr. 4, 1967 22. Each of the rings has integrally formed therewith a suitable fin 34. The top portion of each fin assembly 34 of the radiator assembly 30 is held in spacial relationship relative to the other fin assemblies by a spacing rib 36. The spacing rib 36 is secured to the end fin assemblies by means of screws 33 which pass through overlapping flanges 3-7 of rib 36. The spacing rib 36 includes depending ear portions 38 separated by suitable notches 39, each of which receives a fine assembly 34. The bottom, or lower, portion of each of the fine assemblies is engaged and secured by a pairof corner rail assemblies 40, 42 which are secured to the end in fin assemblies 34 by suitable screws 43 passing through overlapping flanges 44.

The interior of the load resistor housing is formed with a first cylindrical recess '46 which begins at the shoulder 28 and extends through the housing to a first frustoconical step 47. The frusto-conical step 47 communicates with a second cylindrical recess 49 which is reduced in diameter as compared to the first cylindrical recess 46. The second cylindrical recess 49 extends to a second frusto-conical surface 50 which terminates in an oppositely projecting frusto-conical portion 52.

The purpose of this Trepan groove defined by conical Surfaces 50, 52 is to act as a series inductance for the line termination to balance the capacitive effect of the relatively short, fat resistor, which will be subsequently described in detail.

The inwardly projecting conical section 52 terminates .in a surface 53 which is annular in shape and is substantially perpendicular to the axis of the inwardly projecting conical section 52 and perpendicular to the axis of the cylindrical surfaces 46, 49. The inwardly projecting portion 52 includes a recessed cylindrical surface 54 which snugly receives a metallized tapered edge 56 of a resistor assembly 57. The resistor assembly 57 includes a cylindrical substrate member 58 which is preferably formed of high density material of an insulating nature such as beryllium oxide, which is known for its insulating qualities and high thermal conductivity. Any other material exhibiting these qualities would be satisfactory, however.

The end of cylindrical member 58 and the circular surface 53 are wetted with a metallic liquid such as a mixture of thallium, mercury and indium alloy which has good thermal and electrical conductivity. This liquid is an important factor in the proper operation of the termination because it aids the heat transfer from the resistor substrate 58 to the load resistor housing 22. Further, because the housing 22 is grounded to the outer coaxial conductor the liquid provides a good electrical path to the ground.

Preferably, the member 58 has a relatively low aspect ratio, i.e., the ratio of length to diameter. In this particular embodiment, the ratio is unity. A larger ratio would be better electrically and poorer thermally. Conversely, a lower ratio would he better thermally and poorer electrically. This relatively short resistor exhibits a large capacitance to ground, as viewed from coaxial line 12, which capacitance is balanced by the inductance of the previous ly mentioned Trepan groove.

The cylindrical member 58 acts as a subtstrate for a resistive coating 60 which is sprayed, or otherwise formed, as a film or layer on the cylindrical surface of the member '58. In this particular example, the cylindrical member 58 is provided with a small hole 61 therethrough, merely for facilitating machining of the member 58. Resistive coating 60 is connected to a ferrule 62 on the opposite end of the resistor assembly 58 from the metalized tapered edge. The purpose of this ferrule 62 is to provide a good electrical connection between a spring-conductor assembly 65, connected to a coaxial line 12 by connector 13,

and the resistive coating 60. The resistor assembly 57 is held in position in the recess 54- by means of an axial force produced by spring-conductor assembly 65 which has a number of contact spring portions 66 struck from a circular flange which portions engage the metal terminal ferrule 62 (see FIG. 4). The spring-conductor assembly 65 includes a cylindrical section 67 of relatively large diameter which supports the spring portions 66 and abuts a 'section 67, which recess receives a pin 78 of the coaxial line connector 13. Pin 78 is connected to the inner conductor, not shown, of coaxial line 12.

From the foregoing explanation and with reference to the drawing it is apparent that the resistor assembly 57 is axially aligned with the coaxial line 12 and is connected to the inner conductor thereof to form a resistive portion of the line termination; In this particular instance, the termination is designed to terminate a coaxial line having a characteristic impedance of 50 ohms and the resistance of the resistive film or coating 60 is 50 ohms.

Further, this electrical resistance is serially connected to the thermal conductor defined by the load resistor housing 22 and the associated radiator assembly 30.

The configuration of the inner surface of the load resistor housing, i.e., the stepwise tapered recess with frustoconical connecting sections, contributes to the absence of reflections along the coaxial line 12 and to the heat conducting path to the fins 34 nearer the coaxial line 12. The

first frusto-conical surface 47 which separates the first cylindrical section 46 from the second cylindrical recess 49 is located substantially midway along the length of the resistor assembly 57. Further, the refiectionless feature is enhanced by the Trepan groove defined by the pair of oppositely tapering frusto-conical surfaces 50, 52

which connect the second cylindrical recess of the resistor housing 22 to the resistor assembly 57-. In one illustrative embodiment of line termination embodying this invention, a resistor assembly one-inch long and one-inch in diameter supported within a suitable load resistor housing 22 is capable of dissipating 250 watts of electrical power.

In accordance with the patent statutes, the principles of the present invention may be utilized in various ways, numerous modifications and alterations being contemplated, substitution of parts and changes in construction being resorted to as desired, it being understood that the embodiment shown in the drawing is given merely for purposes of illustration and explanation without intending to limit the scope of the claims to the specific details disclosed.

For example, the body 22 is advantageously formed from a single mass of material having high thermal conductivity. In this particular instance, the material is aluminum, however, alloys or other metals preferably having a thermal conductivity of at least 0.4 could beremployed. Further, the substantially solid cylindrical 'resistor substrate is preferably formed of beryllium oxide because this material has a thermal conductivity of the order of 0.4. Other insulating materials having relatively high thermal conductivity could also be employed. Also, the aspect ratio in this particular embodiment of resistor is unity. However, aspect ratios as high as 2 would be satisfactory with substantially solid substrates having high thermal conductivity. Because the use of resistors having smaller aspect ratios than unity, would produce a relatively high capacitive effect upon the coaxial line it is preferred that the ratio be maintained substantially equal to unity or between unity and 2.

What is claimed is: 1. A line termination for a coaxial line having inner and outer conductors comprising:

a metallic load resistor housing adapted to be coupled to the outer conductor of said coaxial line and ineluding a flat endwall portion on the interior thereof; resistor means including a substantially solid substrate member formed of insulating material having good thermal conductivity and a resistive coating thereon mounted in said housing with said coating electrically connected to said housing and with said substrate member thermally connected to said fiat endwall portion; electrically conductive spring means connecting said resistor means to said inner coaxial conductor and applying an axial force to said resistor means to 'force said resistor means against said fiat endwall portion thereby producing good electrical and thermal contact between said resistor means and said housing; and

radiator means coupled to said housing for dissipating and the outer Wall of said recess, said groove facing said coaxial line and defining a re-entrant portion terminating adjacent said cylindrical surface; resistor assembly means supported in axial alignment with said recess and in abutting relationship with said circular surface including means connecting said resistor assembly means to said housing; and

electrically conductive spring means for connecting said resistor assembly means to the inner conductor of said coaxial line and for applying an axial thrust to said resistor assembly means thereby maintaining a thermally and electrically conducting path between said resistor assembly and said housing.

3. A coaxial line termination for terminating the inner and outer conductors of a coaxial line in a reflectionless, heat dissipating termination including:

a load resistor housing formed of metal having a heat conductivity of :at least 0.4 cal./sec./ C./cm.

a recess in said housing, said recess including at least one cylindrical section and a re-entrant, frusto-conical section terminating in a circular surface facing said coaxial line and encircled by a ridge extending toward said coaxial line;

a resistor assembly including a cylindrical resistor formed on a substantially solid substrate having thermal conductivity of at least 0.4 cal./sec./ C./ cm. and an aspect ratio less than 2; and

electrically conducting means supporting and mechanically biasing said resistor against said circular surface and said ridge, said spring means connecting said resistor to said inner conductor, said frustoconical section tapering outwardly from said resistor assembly and outwardly from coaxial line.

4. A line termination for a coaxial line having an outer conductor and a concentric inner conductor comprising:

a resistor assembly including a substantially solid cylindrical member having a heat conductivity greater than 0.3 cal./sec./ C./cm. and having resistive means on the cylindrical surface thereof terminating in a conductive ring;

a load resistor housing formed of metal having a heat conductivity of at least 0.4 cal./sec./ C./cm. and having a recess therein;

said housing including a first frusto-conical section tapering inwardly away from said coaxial line and a frusto-conical resistor assembly mounting portion tapering outwardly toward said coaxial line [for supporting said resistor assembly in axial alignment with said recess, said mounting portion including a rim frictionally engaging said conductive ring;

means defining an endwall of said recess, and a spring assembly extending through said endwall, electrically connecting the inner coaxial conductor to said resistor assembly, mechanically biasing said cylindrical member against said housing mounting portion in thermal conducting relationship and biasing said conductor ring against said rim in electrical conducting relationship.

5. A coaxial line termination according to claim 4 wherein said cylindrical member has a ratio of length to diameter less than two. i

6. A coaxial line termination for a coaxial line having inner and outer conductors comprising:

a generally cylindrical load resistor housing formed from a body of metal having a thermal conductivity of at least 0.4 cal./sec./ C./c1n. and having an axial recess therein with a projection within said recess extending toward the opening of said axial recess and terminating in a circular recess facing said opening;

a substantially solid cylindrical insulating member formed of a material having a thermal conductivity of at least 0.4 cal./sec./ C./cm. positioned with one mounting ring means defining a closure for said recess;

an annular insulating ring supported by and axially aligned with said mounting ring;

a spring-conductor assembly supported by said insulating ring and including spring means applying an axial force to the other end of said resistor; and

a plurality of radiating fins, mounted on, encircling and spaced axially relative to said housing.

7. The termination according to claim 6 wherein said axial recess extends less than half the length of said housing whereby said housing has a circular solid portion defining a thermally conducting path between said one end of said member and said radiating fins.

8. The combination according to claim 7 wherein said member has an aspect ratio less than two.

9. The combination according to claim 7 wherein said member has an aspect ratio substantially equal to unity.

10. The combination according to claim 8 wherein said recess includes a Trepan groove which exhibits an inductive effect to balance the capacitive efiect of said resistor means.

11. The combination according to claim 8 wherein said recess tapers inwardly to define thermally conductive paths of greater cross-sectional area nearer said resistor.

RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner. 

3. A COAXIAL LINE TERMINATION FOR TERMINATING THE INNER AND OUTER CONDUCTORS OF A COAXIAL LINE IN A REFLECTIONLESS, HEAT DISSIPATING TERMINATION INCLUDING: A LOAD RESISTOR HOUSING FORMED OF METAL HAVING A HEAT CONDUCTIVITY OF AT LEAST 0.4 CAL./SEC./*C./CM.3; A RECESS IN SAID HOUSING, SAID RECESS INCLUDING AT LEAST ONE CYLINDRICAL SECTION AND A RE-ENTRANT, FRUSTO-CONICAL SECTION TERMINATING IN A CIRCULAR SURFACE FACING SAID COAXIAL LINE AND ENCIRCLED BY A RIDGE EXTENDING TOWARD SAID COAXIAL LINE; A RESISTOR ASSEMBLY INCLUDING A CYLINDRICAL RESISTOR FORMED ON A SUBSTANTIALLY SOLID SUBSTRATE HAVING THERMAL CONDUCTIVITY OF AT LEAST 0.4 CAL./SEC./*C./ CM.3 AND AN ASPECT RATIO LESS THAN 2; AND ELECTRICALLY CONDUCTING MEANS SUPPORTING AND MECHANICALLY BIASING SAID RESISTOR AGAINST SAID CIRCULAR SURFACE AND SAID RIDGE, SAID SPRING MEANS CONNECTING SAID RESISTOR TO SAID INNER CONDUCTOR, SAID FRUSTOCONICAL SECTION TAPERING OUTWARDLY FROM SAID RESISTOR ASSEMBLY AND OUTWARDLY FROM COAXIAL LINE. 